A recent analysis by the U.S. Preventive Services Task Force suggests that aspirin might lower your risk of certain cancers, especially colon cancer if it's taken long term. But you shouldn't take aspirin for cancer prevention alone. That's because the drug also poses risks—in particular the risk of dangerous bleeding in the stomach and brain—that may outweigh its possible protective effect against cancer.   

But if you and your doctor decide that taking a daily, low-dose aspirin (81 mg, or a "baby aspirin") is a good way to reduce your risk of heart disease, then think of a reduced risk of colon cancer as a bonus.

Considerable research going back decades shows that taking low-dose aspirin can help prevent heart attacks and ischemic strokes (the kind caused by blood clots) in people at high risk for cardiovascular disease. Now, researchers at the Preventive Services Task Force, an independent, volunteer panel of experts in prevention and evidenced-based medicine, have looked back at those studies to see what effect aspirin might have had on the risk of cancer. Combined data from three large studies involving 47,464 people suggested that, compared to people who didn’t take aspirin, those who did reduced their risk of colon cancer by about 40 percent, but only 10 to 19 years after they started taking the drug.

Earlier research suggests that regular aspirin use may also help prevent cancers of the breast, esophagus, ovaries, stomach, and prostate. But current evidence is not strong enough to draw conclusions about anything other than colon cancer, according to the analysis conducted for the task force.

Uncertain Benefits vs. Known Harms

Encouraging results make a compelling case for ongoing, high-quality research looking at specific cancers, says Evelyn P. Whitlock, M.D., director of Kaiser Permanente Research Affiliates’ Evidence-based Practice Center in Portland, Ore. and one of the authors of the task force analysis. But current evidence doesn’t support taking aspirin solely to prevent colon cancer.

The evidence to date has to be “interpreted cautiously,” says Whitlock “because it comes largely from a small set of older trials on cardiovascular disease prevention that were not set up to study the effect of aspirin on cancer.”

The studies were typically lacking in key information, such as participants’ cancer risk, for example, and some were too short to capture the long-term effects of aspirin.  Some trials also used much higher doses of aspirin than currently recommended for daily therapy, making it unclear whether lower doses would work as well to prevent colon cancer.

That uncertain benefit is outweighed by well-known harms, says Whitlock. Low-dose aspirin carries a rare, but serious risk of bleeding that can result in hospitalization, the need for a transfusion, or even death.

Other Ways to Prevent Colon Cancer

Whether you take aspirin, you can still take other steps to help reduce your colon cancer risk, says Marvin M. Lipman, M.D., Consumer Report's chief medical adviser.

"Regularly eating fiber-rich fruits and vegetables, while limiting red meat may be helpful in colon cancer prevention," says Lipman.

He also notes that moderating your alcohol consumption, maintaining a healthy weight, exercising at least 30 minutes daily, and not smoking can also lower risk. Paying attention to all those good lifestyle measures can be good for your heart, as well.

The Preventive Services Task Force also suggests regular screenings tests such as a colonoscopy every 10 years starting at age 50, which can detect cancer in its earliest, treatable stages, as well as precancerous growths that can be removed before they develop into cancer. Read more about options for colon cancer screening.